TWI423214B - Pixel driving circuit and pixel driving method - Google Patents

Description

Pixel driving circuit and pixel driving method

The present invention relates to a driving circuit and a driving method, and more particularly to a pixel driving circuit and a pixel driving method.

Recently, due to advances in technology, the brightness and lifetime of organic light emitting diode (OLED) materials have been greatly improved, and they have high contrast, high viewing angle and low power consumption, so organic light emitting The polar display is considered to be one of the most promising flat display technologies in the future.

In general, in high-end applications, organic light-emitting diode displays are mostly driven in an active mode (AM) for higher resolution and less noise interference. Driven by the active mode, each pixel of the organic light emitting diode display needs to be provided with a thin film transistor to drive the corresponding organic light emitting diode to emit light. However, for a large-area process, the thin film transistor is prone to characteristic variation. This phenomenon is common in the threshold voltage of the device. The possible source is the variation of the process or the electrical offset of the component. effect. Therefore, how to compensate for the variation of the threshold voltage to achieve uniform brightness output has become an important issue.

FIG. 1 illustrates a pixel driving circuit conventionally used to solve a threshold voltage variation. Referring to FIG. 1, in the conventional pixel driving circuit, in addition to the driving transistor DTFT for driving pixels, the pixel driving circuit further includes switching transistors SW1 SWSW3 to memorize the criticality of driving the TFT DTFT. The voltage is operated as follows. First, at period T1, voltage V _DD precharges the gate of the driving transistor DTFT. Thereafter, at the period T2, the signal DT is set to the data voltage V _DATA , and the gate voltage of the driving transistor DTFT is discharged through the switching transistors SW1 and SW2 until the voltage at the point is equal to the threshold voltage V _T plus the data voltage V Discharge is stopped at _DATA (V _T +V _DATA ) and the critical voltage value is recorded. Finally, the signal TNO turns on the switching transistor SW3 to cause the voltage V _{DD to} start driving the organic light emitting diode OLED.

It should be noted that although this design is suitable for an enhancement mode transistor, when the transistor element is a depletion mode transistor, in the above period T2, the target voltage of the predetermined discharge is V _T + V _DATA will be smaller than the threshold voltage V _T , so that only the gate voltage of the driving transistor can be discharged to the level of the data voltage V _DATA , and the function of the memory threshold voltage is lost. Therefore, when the transistor element is a depleted transistor, the display quality of the display using the above pixel driving circuit is still poor. In the prior art, many other techniques for compensating component threshold voltage variations are mostly designed using this principle, so the same problem is still encountered when using a depleted transistor as a pixel component.

An exemplary embodiment of the present invention provides a pixel driving circuit. When the transistor component of the pixel driving circuit is a depleted transistor, the pixel driving circuit can still operate normally and compensate for the critical voltage variation of the driving transistor.

An exemplary embodiment of the present invention provides a pixel driving method suitable for A pixel drive circuit. When the transistor component of the pixel driving circuit is a depleted transistor, the pixel driving method can still compensate for the threshold voltage variation of the driving transistor to improve the uniformity of the brightness of the pixel panel.

An exemplary embodiment of the present invention provides a pixel driving circuit adapted to drive a light emitting element. The pixel driving circuit includes a first driving unit, a second driving unit, and an adjusting unit. The first driving unit is configured to drive the light emitting element, wherein the first driving unit comprises a first transistor. The second driving unit is configured to provide a data voltage to the first transistor, so that the first driving unit drives the light emitting element according to the data voltage. The adjusting unit is configured to adjust a gate voltage of the first transistor, wherein the adjusting unit includes a set capacitor and a second transistor, and the set capacitor is coupled in series with the second transistor to the first driving unit and the second driving unit between.

In an exemplary embodiment of the invention, the set capacitor is used to adjust a gate voltage of the first transistor.

In an exemplary embodiment of the invention, the pixel driving circuit further includes a storage capacitor. The storage capacitor is coupled between the first driving unit and the second driving unit for storing a data voltage to one of the gates of the first transistor.

In an exemplary embodiment of the invention, the first driving unit further includes a third transistor. The third transistor has a gate, a first source/drain, and a second source/drain. The gate of the third transistor is controlled by a first control signal. The first source/drain of the third transistor is coupled to a first voltage. The second source/drain of the third transistor is coupled to one of the first source/drain of the first transistor. The second source/drain of the first transistor is coupled to the first end of the light emitting element, and the second end of the light emitting element is coupled to a second control signal.

In an exemplary embodiment of the invention, the second driving unit includes a fourth transistor and a fifth transistor. The fourth transistor has a gate, a first source/drain, and a second source/drain. The gate of the fourth transistor is controlled by a third control signal. The first source/drain of the fourth transistor receives the data voltage. The second source/drain of the fourth transistor is coupled to the gate of the first transistor. The fifth transistor has a gate, a first source/drain, and a second source/drain. The gate of the fifth transistor is controlled by a fourth control signal. The first source/drain of the fifth transistor receives the data voltage. The second source/drain of the fifth transistor is coupled to the second source/drain of the first transistor. Here, the adjustment unit has a first end and a second end. The first end of the adjustment unit is coupled to the gate of the first transistor, and the second end of the adjustment unit is coupled to the source/drain of the first transistor.

In an exemplary embodiment of the present invention, the first control signal, the second control signal, the third control signal, and the fourth control signal are at a high level during a precharge period. During a set period, the first control signal and the third control signal are at a low level, and the second control signal and the fourth control signal are at a high level. During a lighting period, the first control signal is at a high level, and the second control signal, the third control signal, and the fourth control signal are at a low level.

In an exemplary embodiment of the present invention, the first transistor, the second transistor, the third transistor, the fourth transistor, and the fifth transistor include at least one depletion transistor.

In an exemplary embodiment of the invention, the first source/drain of the fourth transistor further receives a reference voltage.

In an exemplary embodiment of the present invention, the first driving unit is further included Includes a third transistor. The third transistor has a gate, a first source/drain, and a second source/drain. The gate of the third transistor is controlled by a first control signal. The second source/drain of the third transistor is coupled to a second voltage. The first end of the light-emitting element is coupled to a second control signal, and the second end of the light-emitting element is coupled to one of the first source/drain of the first transistor. One of the first source/drain of the first transistor is coupled to the first source/drain of the third transistor.

In an exemplary embodiment of the invention, the second driving unit includes a fourth transistor and a fifth transistor. The fourth transistor has a gate, a first source/drain, and a second source/drain. The gate of the fourth transistor is controlled by a third control signal. The first source/drain of the fourth transistor receives the data voltage. The second source/drain of the fourth transistor is coupled to the gate of the first transistor. The fifth transistor has a gate, a first source/drain, and a second source/drain. The gate of the fifth transistor is controlled by a fourth control signal. The first source/drain of the fifth transistor receives the data voltage. The second source/drain of the fifth transistor is coupled to the first source/drain of the first transistor. Here, the adjustment unit has a first end and a second end. The first end of the adjusting unit is coupled to the gate of the first transistor, and the second end of the adjusting unit is coupled to the second end of the light emitting element.

In an exemplary embodiment of the present invention, the first control signal is at a low level during a precharge period, and the second control signal, the third control signal, and the fourth control signal are at a high level. During a set period, the first control signal, the second control signal, and the third control signal are at a low level, and the fourth control signal is at a high level. During a lighting period, the first control signal and the second control signal are at a high level, and the third control signal and the fourth control signal are at a low level.

Another exemplary embodiment of the present invention provides a pixel driving method suitable for a pixel driving circuit. The pixel driving circuit is configured to drive a light emitting component, and includes a first driving unit, a second driving unit, and an adjusting unit. The pixel driving method includes the following steps. The light emitting element is driven by the first driving unit, wherein the first driving unit comprises a first transistor. A data voltage is supplied to the first transistor by the second driving unit, so that the first driving unit drives the light emitting element according to the data voltage. Adjusting the gate voltage of the first transistor by adjusting the unit, wherein the adjusting unit includes a set capacitor and a second transistor, and the set capacitor is coupled in series with the second transistor to the first driving unit and the second driving unit between.

In an exemplary embodiment of the present invention, in the step of adjusting the gate voltage of the first transistor, the gate voltage of the first transistor is adjusted by setting a capacitance.

In an exemplary embodiment of the invention, the pixel driving circuit further includes a storage capacitor. The storage capacitor is coupled between the first driving unit and the second driving unit. The pixel driving method further includes. The storage voltage is stored in one of the gates of the first transistor by the storage capacitor.

In an exemplary embodiment of the present invention, the adjusting unit has a first end and a second end. In the step of providing the data voltage to the first transistor, the first end and the second end of the adjusting unit are respectively charged to the data voltage and a first voltage during a pre-charging period.

In an exemplary embodiment of the present invention, in the step of adjusting the gate voltage of the first transistor, the first end of the adjustment unit is discharged by the second driving unit and the adjusting unit during a set period, Compensating the first crystal The critical voltage value of the body.

In an exemplary embodiment of the present invention, in the step of driving the light-emitting element, during a light-emitting period, the first transistor is turned on according to the threshold voltage value of the first transistor memorized by the set capacitance to be driven by the first voltage. Light-emitting element.

In an exemplary embodiment of the present invention, in the step of providing a data voltage to the first transistor, a reference voltage is further provided to the first transistor.

Based on the above, in an exemplary embodiment of the present invention, the pixel driving circuit and the pixel driving method can be used to compensate for unevenness or drift of the driving transistor threshold voltage to provide a relatively uniform current of the light emitting element. In addition, in the exemplary embodiment of the present invention, even if the pixel driving circuit is composed of a depleted transistor, the threshold voltage compensation function of the driving transistor can still operate normally.

The above described features and advantages of the present invention will be more apparent from the following description.

Recently, the realization of soft electronic applications has become possible due to the discovery of new semiconductor materials. These materials are, for example, organic semiconductor materials or zinc oxide semiconductor materials, which can be fabricated over a large area at low temperatures, and are therefore particularly suitable for fabrication on flexible substrates. However, transistors on plastic flexible substrates often have the property of being biased toward depleted elements. That is, the transistor cannot be effectively turned off when the transistor gate is unbiased. Due to the above characteristics, the existing pixel driving circuit is prone to error in function, and cannot compensate for the variation of the threshold voltage. The brightness of the panel is not uniform.

Therefore, at least in order to solve the problem of brightness uniformity of the above flexible panel display, in an exemplary embodiment of the present invention, the pixel driving circuit and the pixel driving method can overcome the failure of the conventional pixel driving circuit to be applied to a depleted transistor. The problem is to get a better quality display.

In the following exemplary embodiments, an organic light-emitting diode will be used as the light-emitting element, and any person skilled in the art will recognize that the organic light-emitting diode is not intended to limit the light-emitting element of the present invention. Meanwhile, the present invention is not limited to the pixel driving circuit used in the flexible panel display, and any pixel driving circuit used in the display using the light emitting element as the panel pixel is in the scope of the present invention.

2A is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention. 2B is a circuit diagram of the adjustment unit of FIG. 2A. Referring to FIG. 2A and FIG. 2B, the pixel driving circuit 200 of the present embodiment is adapted to drive a light emitting device D, which includes a first driving unit 210, a second driving unit 220, an adjusting unit 230, and a storage capacitor C. _ST . The adjustment unit 230 includes a set capacitor C _SET and a transistor T ₂ , which are coupled in series between the first driving unit 210 and the second driving unit 220 .

In detail, in the present embodiment, the light-emitting element D is, for example, an organic light-emitting diode, which is one of the pixels on the flexible substrate of the flexible panel display. The first driving unit 210 drives the light emitting element D by driving the transistor T ₁ . The second driving unit 220 is configured to provide a data voltage V _DATA to the driving transistor T ₁ , so that the driving transistor T ₁ can drive the light emitting element D according to the data voltage V _DATA . In addition, the storage capacitor C _{ST is} coupled between the first driving unit 210 and the second driving unit 220 to store the data voltage V _DATA at the gate of the driving transistor T ₁ .

It should be noted that the adjusting unit 230 of this embodiment can be used to adjust the gate voltage of the driving transistor T ₁ (that is, the voltage of the node n ₁ ). Here, the transistor T _{2 of the} adjusting unit 230 is controlled by the control signal SET and is turned on or off during different operations of the pixel driving circuit 200 to provide an adjustment of the gate voltage of the adjustment driving transistor T ₁ . path. Therefore, when the transistor T ₂ is turned on, the set capacitance C _SET can adjust the gate voltage of the driving transistor T1 and memorize the threshold voltage value of the driving transistor T ₁ .

Accordingly, in the present embodiment, by the action of adjustment means 230, the pixel driving circuit may compensate the driving transistor T 200 ₁ or uneven threshold voltage drift, the light emitting element D to provide more uniform current.

Further, the first driving unit 210 further includes a transistor T ₃ . The gate of transistor T ₃ is controlled by control signal EM (first control signal). One source/drain of the transistor T ₃ is coupled to a high level voltage V _DD (first voltage). The other source/drain of the transistor T ₃ is coupled to one of the source/drain of the driving transistor T ₁ . In addition, the other source/drain of the driving transistor T ₁ is coupled to the anode of the light-emitting element D, and the cathode of the light-emitting element D is coupled to the control signal VL (second control signal).

The second driving unit 220 includes a transistor T ₄ and a transistor T ₅ . The gate of transistor T ₄ is controlled by a control signal CH (third control signal). One source/drain of the transistor T ₄ receives the data voltage V _DATA . The other source/drain of the transistor T ₄ is coupled to the gate of the driving transistor T ₁ . Therefore, when the control signal CH is at a high level, the transistor T ₄ is turned on, thereby providing the data voltage V _DATA to the driving transistor T ₁ .

In addition, the gate of the transistor T ₅ is controlled by the control signal SET (fourth control signal). One source/drain of the transistor T ₅ receives the data voltage V _DATA . The other source/drain of the transistor T ₅ is coupled to the source/drain of the driving transistor T ₁ . Here, one end of the adjusting unit 230 is coupled to the gate of the driving transistor T ₁ by the node n ₁ , and the other end of the adjusting unit 230 is coupled to the other source/drain of the driving transistor T ₁ by the node n _{2 .} .

FIG. 3 is a timing chart showing driving of each control signal of the pixel driving circuit of FIG. 2A. Referring to FIG. 2A, FIG. 2B and FIG. 3, in the embodiment, the transistor elements of the pixel driving circuit 200 are, for example, n-type transistors, and the two ends of the adjusting unit 230 are respectively connected to the nodes n ₁ and n _{2 .} .

Taking the driving timing of the control signal of FIG. 3 as an example, the pixel driving circuit 200 of this embodiment can be divided into the following several operating phases:

(1) Pre-charge period:

In the pre-charging period P1, the control signals EM, VL, CH, and SET are all at a high level, so the transistors T ₁ -T ₅ are all in an on state, so that the second driving unit 220 can use the transistor T ₃ to data The voltage V _{DATA is} set to the node n ₁ . In addition, the voltage of the node n ₂ can be set to be close to the high level voltage V _DD via the transistor T ₁ via the adjustment of the transistor size. Here, the control signal VL at a high level is used to prevent the light-emitting element D from leaking.

(2) Setting period:

During the set period P2, the control signals EM and CH are at a low level, and the control signals VL and SET are at a high level. Thus, a low level of control signal CH off transistor T _4, and further such that the node n ₁ becomes a floating state. Meanwhile, the low level of the control signal EM also closed transistor T _3, thereby cut off the high level voltage V _DD. In the setting period P2, since the control signals VL and SET are at a high level, the voltage of the node n ₁ is discharged through the transistor T ₂ , the capacitor C _SET and the transistors T ₁ , T _{5 of the} adjusting unit 230 until the node n ₁ The discharge is stopped when the voltage is equal to the threshold voltage V _T plus the data voltage V _DATA (V _T +V _DATA ). At this time, since the driving transistor T ₁ is turned off, the node n _{1 is} prevented from being discharged. Therefore, the threshold voltage information of the driving transistor T ₁ is memorized in the storage capacitor C _ST or the set capacitor C _SET .

(3) During the illuminating period:

In the light-emitting period P3, except for the control signal EM being at a high level, the control signals VL, CH, and SET are all at a low level. The high level control signal EM is used to provide a high level voltage V _DD to the light emitting element D (ie, panel pixels). In addition, the control signal SET needs to be at a low level to turn off the transistor T ₂ to prevent the voltage change of the node n ₂ from affecting the voltage value of the node n ₁ . The control signal VL becomes a low level, so that the light-emitting element D can start to emit light.

It can be seen from the above operation stage that since the threshold voltage information of the driving transistor T ₁ has been memorized in the storage capacitor C _ST or the set capacitor C _SET , the unevenness of the output current of the driving transistor T ₁ can be improved. Therefore, in the present embodiment, even if the pixel driving circuit 200 is composed of a depleted transistor, the threshold voltage compensation function of the driving transistor T ₁ can still operate normally.

4 is a diagram showing the relationship between the output current and the data voltage of a conventional pixel driving circuit. FIG. 5 is a diagram showing the relationship between the output current and the data voltage of the pixel driving circuit of FIG. 2A. FIG. 6 is a graph showing the comparison of the uniformity of the output current of the pixel driving circuit of FIG. 2A and the conventional pixel driving circuit.

Please refer to FIG. 4 to FIG. 6. FIG. 4 and FIG. 5 are diagrams showing the relationship between the output current and the data voltage obtained by simulating the pixel driving circuit and the pixel driving circuit of FIG. 2A by using the simulation engine spectre. The components in the pixel drive circuit use a-IGZO thin film transistor components as a reference for the component model parameters. The measured threshold voltage V _T of the driving transistor is -2.5 V, and the threshold voltage V _T variation is assumed to be 1 V.

The results of the output current versus data voltage using a conventional pixel drive circuit are shown in FIG. In the conventional pixel driving circuit, due to the use of the depletion transistor, the function of the original compensation threshold voltage variation is invalid, resulting in a phenomenon in which the output current is uneven as shown in FIG.

Conversely, using the pixel drive circuit of Figure 2A, this problem can be successfully overcome. The result of the output current versus data voltage of the pixel drive circuit 200 of FIG. 2A is shown in FIG. As can be seen from Fig. 5, the threshold voltage V _{T of the} driving transistor is under the variation of plus or minus 1 V, and the output current has a fairly good uniformity. That is, the output currents are nearly equal under different threshold voltages.

In Fig. 6, the non-uniformity of the output current obtained by the conventional pixel driving circuit and the pixel driving circuit of Fig. 2A is compared. As can be seen from FIG. 6, the pixel driving circuit proposed by the exemplary embodiment of the present invention can greatly improve the unevenness of the output current of the driving transistor, and can be less than 4% here.

It should be noted that, in an exemplary embodiment of the present invention, when the transistor components of the pixel driving circuit are all depleted transistors, the pixel driving circuit can operate normally and compensate for the critical voltage variation of the driving transistor, but The invention is not limited to this. In other embodiments, when the transistor component of the pixel driving circuit is composed of a depleted or lifted transistor, the pixel driving circuit remains It can operate normally and compensate for the critical voltage variation of the drive transistor.

FIG. 7 is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention. Referring to FIG. 7, in the embodiment, the transistor component of the pixel driving circuit 700 is, for example, a depletion type or a lift type transistor.

The difference between the pixel drive circuit 700 of the present embodiment and the pixel drive circuit 200 of FIG. 2A is that, for example, the second drive unit 720 of the present embodiment receives a reference voltage V _{REF in} addition to the data voltage V _DATA . In order to ensure that when the driving transistor T ₁ is a lifting type transistor, the driving transistor T ₁ during the setting period can still be kept in the off state, so that the threshold voltage information of the driving transistor T ₁ can be memorized in the storage capacitor C _{ST .} Or set the capacitor C _SET .

In detail, in the present embodiment, one source/drain of the transistor T ₄ receives the data voltage V _DATA and the reference voltage V _REF (V _DATA + V _REF ). Therefore, when the control signal CH is at a high level, the transistor T ₄ is turned on, thereby providing a voltage V _DATA +V _REF to the node n ₁ . In addition, one source/drain of the transistor T ₅ receives only the data voltage V _DATA .

Therefore, under this design architecture, when node n _{1 is} discharged during the set period, its voltage can still be higher than the data voltage V _DATA until the voltage of node n ₁ is equal to the threshold voltage V _T plus the data voltage V _DATA (V Discharge is stopped only when _T +V _DATA ). At this time, the threshold voltage information of the driving transistor T ₁ is memorized in the storage capacitor C _ST or the set capacitor C _SET .

Therefore, in the present embodiment, through a proper design, the pixel driving circuit composed of the depletion type or the lifting type crystal element can be normally operated and compensated for the threshold voltage of the driving transistor.

In addition, the same or similar parts of the pixel driving circuit 700 of the present embodiment and the pixel driving circuit 200 of FIG. 2A can obtain sufficient teaching, suggestion and implementation instructions from the description of the exemplary embodiments of FIGS. 2A to 3 . Therefore, I will not repeat them.

In the above embodiment, the crystal elements of the pixel driving circuits 200, 700 are, for example, n-type transistors, but the present invention is not limited thereto. In other embodiments, the transistor elements of the pixel drive circuit may also be, for example, p-type transistors.

FIG. 8A is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention. FIG. 8B is a circuit diagram of the adjusting unit of FIG. 8A. Referring to FIG. 8A and FIG. 8B, the pixel driving circuit 800 of the present embodiment is adapted to drive a light-emitting component D, which includes a first driving unit 810, a second driving unit 820, an adjusting unit 830, and a storage capacitor C. _ST .

The adjustment unit 830 includes a set capacitor C _SET and a transistor T ₂ , which are coupled in series between the first driving unit 810 and the second driving unit 820 . One end of the adjusting unit 830 is coupled to the gate of the driving transistor T ₁ by the node n ₁ , and the other end of the adjusting unit 830 is coupled to the other source/drain of the driving transistor T ₁ by the node n ₂ .

Similarly, the adjusting unit 830 of the present embodiment can be used to adjust the gate voltage of the driving transistor T ₁ (that is, the voltage of the node n ₁ ). Accordingly, in the present embodiment, by the action of adjustment means 830, the pixel driving circuit 800 may compensate the driving transistor T ₁ or uneven threshold voltage drift, the light emitting element D to provide more uniform current.

It should be noted that, in this embodiment, one end of the adjusting unit 830 is connected to the cathode of the light-emitting element D via the node n ₂ , and the anode of the light-emitting element D is coupled to the control signal VH (the fifth control signal).

Further, the first driving unit 810 includes a driving transistor T ₁ and a transistor T ₃ . The gate of transistor T ₃ is controlled by control signal EM. One source/drain of the transistor T ₃ is coupled to ground (second voltage). The other source/drain of the transistor T ₃ is coupled to one of the source/drain of the driving transistor T ₁ . In addition, the other source/drain of the driving transistor T ₁ is coupled to the cathode of the light-emitting element D via the node n ₂ .

The second driving unit 820 includes transistors T ₄ and T ₅ . The gate of transistor T ₄ is controlled by control signal CH. One source/drain of the transistor T ₄ receives the data voltage V _DATA . The other source/drain of the transistor T ₄ is coupled to the gate of the driving transistor T ₁ . The gate of transistor T ₅ is controlled by control signal SET. One source/drain of the transistor T ₅ receives the data voltage V _DATA . The other source/drain of the transistor T ₅ is coupled to the source/drain of the driving transistor T ₁ and the transistor T ₃ .

Fig. 9 is a timing chart showing the driving of each control signal of the pixel driving circuit of Fig. 8A. Referring to FIG. 8A, FIG. 8B and FIG. 9 , in the embodiment, the transistor elements of the pixel driving circuit 800 are both p-type transistors, and the two ends of the adjusting unit 830 are respectively connected to the nodes n ₁ and n _{2 .} .

Taking the driving timing of the control signal of FIG. 9 as an example, the pixel driving circuit 800 of this embodiment can be divided into the following operation stages:

(1) Pre-charge period:

First, in the precharge period P1, the control signals CH, VH, and SET are at a high level, so the data voltage V _DATA can be set to the node n ₁ via the transistor T ₄ and supplied via the light-emitting element D, the node n ₂ The voltage can be set to be higher than the voltage of node n ₁ . In addition, the control signal EM is at a low level at this stage to reduce the extra leakage path.

(2) Setting period:

In the set period P2, the control signals CH and VH are at a low level, so that the node n _{1 is in} a floating state, and the voltage of the node n ₂ is not charged by the light-emitting element D. The control signal EM is also at a low level, thus blocking the path of the ground. In the setting period P2, since the control signal SET is at a high level, the voltage of the node n ₁ is discharged through the transistor T ₂ , the capacitor C _SET and the transistors T ₁ , T _{5 of the} adjusting unit 230 until the voltage of the node n ₁ The discharge is stopped when the threshold voltage V _T is equal to the data voltage V _DATA (V _T +V _DATA ). At this time, since the driving transistor T ₁ is turned off, the node n _{1 is} prevented from being discharged. Therefore, the threshold voltage information of the driving transistor T ₁ is memorized in the storage capacitor C _ST or the set capacitor C _SET .

(3) During the illuminating period:

P3 during light emission, the control signals EM, VH is the high level, the transistor turned on T _3, to provide a ground path to the light emitting element D. In addition, the control signal SET needs to be at a low level to turn off the transistor T ₂ to prevent the voltage change of the node n ₂ from affecting the voltage value of the node n ₁ .

It can be seen from the above operation stage that since the threshold voltage information of the driving transistor T ₁ has been memorized in the storage capacitor C _ST or the set capacitor C _SET , the unevenness of the output current of the driving transistor T ₁ can be improved. Therefore, in the present embodiment, even if the pixel driving circuit 800 is composed of a depleted transistor, the threshold voltage compensation function of the driving transistor T ₁ can still operate normally.

In addition, the pixel driving circuit 800 of the embodiment and the pixel driving of FIG. 2A The same or similar parts of the dynamic circuit 200 can be sufficiently taught, suggested and implemented by the description of the exemplary embodiments of FIG. 2A to FIG. 3, and therefore will not be described again.

Similarly, in an exemplary embodiment of the present invention, when the transistor elements of the pixel driving circuit are all depleted transistors, the pixel driving circuit can operate normally and compensate for the critical voltage variation of the driving transistor, but the present invention Not limited to this. In other embodiments, when the transistor component of the pixel driving circuit is composed of a depleted or lifted transistor, the pixel driving circuit can still operate normally and compensate for the threshold voltage variation of the driving transistor.

FIG. 10 is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention. Referring to FIG. 10, in the embodiment, the transistor component of the pixel driving circuit 1000 is, for example, a depleted or lifted transistor, except that the transistor elements are, for example, p-type transistors.

The difference between the pixel driving circuit 1000 of the present embodiment and the pixel driving circuit 800 of FIG. 8A is that, for example, the second driving unit 1020 of the present embodiment receives a reference voltage V _{REF in} addition to the data voltage V _DATA . In order to ensure that when the driving transistor T ₁ is a lifting type transistor, the driving transistor T ₁ during the setting period can still be kept in the off state, so that the threshold voltage information of the driving transistor T ₁ can be memorized in the storage capacitor C _{ST .} Or set the capacitor C _SET .

Therefore, under this design architecture, when node n _{1 is} discharged during the set period, its voltage can still be higher than the data voltage V _DATA until the voltage of node n ₁ is equal to the threshold voltage V _T plus the data voltage V _DATA (V Discharge is stopped only when _T +V _DATA ). At this time, the threshold voltage information of the driving transistor T ₁ is memorized in the storage capacitor C _ST or the set capacitor C _SET .

Therefore, in the present embodiment, through a proper design, the pixel driving circuit composed of the depletion type or the lifting type crystal element can be normally operated and compensated for the threshold voltage of the driving transistor.

In addition, the same or similar parts of the pixel driving circuit 1000 of the present embodiment and the pixel driving circuit 800 of FIG. 8A can obtain sufficient teaching, suggestion and implementation instructions from the description of the exemplary embodiments of FIGS. 8A to 9 . Therefore, I will not repeat them.

FIG. 11 is a flow chart showing the steps of a pixel driving method according to an exemplary embodiment of the present invention. Referring to FIG. 2A to FIG. 3 and FIG. 11, the pixel driving method of this embodiment includes the following steps.

In step S1100, the data voltage V _{DATA is} supplied to the driving transistor T ₁ by the second driving unit 220 to cause the first driving unit 210 to drive the light emitting element D according to the material voltage V _DATA . That is, during the pre-charging period P1, the first terminal (node n ₁ ) and the second terminal (node n ₂ ) of the adjusting unit 230 are respectively charged to the data voltage V _DATA and the high-level voltage V _DD .

In step S1102, the adjustment unit 230 by adjusting the gate voltage of the driving transistor T _1, ie. That is, the period P2 is set, and the drive unit 220 by the second adjustment unit 230, the adjustment unit 230 of a first end of the discharge drive transistor to compensate for the threshold voltage T _1.

In step S1104, the light-emitting element D is driven by the first driving unit 210. That is, the light emission period P3, the voltage threshold value is set based on capacitor C _SET memorized driving transistor T _1, ie, on drive transistor T _1, to a high level by driving the light emitting element voltage V _DD D.

In addition, the pixel driving method of the embodiment of the present invention can be sufficiently taught, suggested, and implemented by the description of the exemplary embodiments of FIGS. 2A-10, and thus will not be described again.

In summary, in an exemplary embodiment of the present invention, the pixel driving circuit and the pixel driving method can be used to compensate for unevenness or drift of the driving transistor threshold voltage to provide a relatively uniform current of the light emitting element. In addition, in the exemplary embodiment of the present invention, regardless of the type of transistor structure of the pixel driving circuit, the threshold voltage compensation function of the driving transistor can operate normally.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

200, 700, 800, 1000‧‧‧ pixel drive circuit

210, 710, 810, 1010‧‧‧ first drive unit

220, 720, 820, 1020‧‧‧ second drive unit

230, 730, 830, 1030‧‧‧ adjustment unit

T ₂ ~T ₅ ‧‧‧O crystal

SW1~SW3‧‧‧Switching transistor

DTFT, T ₁ ‧‧‧ drive transistor

C _SET ‧‧‧Set capacitor

C _ST ‧‧‧ storage capacitor

OLED‧‧ Organic Light Emitting Diode

D‧‧‧Lighting elements

V _DATA ‧‧‧ data voltage

V _T ‧‧‧ threshold voltage

V _REF ‧‧‧reference voltage

V _DD ‧‧‧ voltage

n ₁ , n ₂ ‧‧‧ nodes

EM, CH, SET, VL, VH‧‧‧ control signals

TNO, SLT, CTD, DT‧‧‧ signals

P1‧‧‧Precharge period

P2‧‧‧Setting period

P3‧‧‧Lighting period

T1, T2‧‧ cycle

S1100, S1102, S1104‧‧‧ pixel driving method steps

FIG. 1 illustrates a pixel driving circuit conventionally used to solve a threshold voltage variation.

2A is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention.

2B is a circuit diagram of the adjustment unit of FIG. 2A.

FIG. 3 is a timing chart showing driving of each control signal of the pixel driving circuit of FIG. 2A.

4 is a diagram showing the relationship between the output current and the data voltage of a conventional pixel driving circuit.

Figure 5 is the output current vs. data voltage of the pixel driving circuit of Figure 2A relation chart.

FIG. 6 is a graph showing the comparison of the uniformity of the output current of the pixel driving circuit of FIG. 2A and the conventional pixel driving circuit.

FIG. 7 is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention.

FIG. 8A is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention.

FIG. 8B is a circuit diagram of the adjusting unit of FIG. 8A.

Fig. 9 is a timing chart showing the driving of each control signal of the pixel driving circuit of Fig. 8A.

FIG. 10 is a block diagram of a pixel driving circuit according to an exemplary embodiment of the present invention.

FIG. 11 is a flow chart showing the steps of a pixel driving method according to an exemplary embodiment of the present invention.

200‧‧‧ pixel drive circuit

210‧‧‧First drive unit

220‧‧‧Second drive unit

230‧‧‧Adjustment unit

T ₁ ‧‧‧Drive transistor

T ₃ ~T ₅ ‧‧‧O crystal

C _ST ‧‧‧ storage capacitor

D‧‧‧Lighting elements

V _DATA ‧‧‧ data voltage

V _DD ‧‧‧ voltage

n ₁ , n ₂ ‧‧‧ nodes

VL‧‧‧ control signal

Claims (20)

A pixel driving circuit is adapted to drive a light emitting element, the pixel driving circuit comprising: a first driving unit for driving the light emitting element, wherein the first driving unit comprises a first transistor; a second driving a unit for providing a data voltage to the first transistor, so that the first driving unit drives the light emitting element according to the data voltage; and an adjusting unit for adjusting a gate voltage of the first transistor, wherein The adjusting unit includes a set capacitor and a second transistor, and the set capacitor is coupled in series with the second transistor between the first driving unit and the second driving unit. The pixel drive circuit of claim 1, wherein the set capacitor is used to adjust a gate voltage of the first transistor. The pixel driving circuit of claim 1, further comprising a storage capacitor coupled between the first driving unit and the second driving unit for storing the data voltage in the first transistor One of the gates. The pixel driving circuit of claim 1, wherein the first driving unit further comprises: a third transistor having a gate, a first source/drain, and a second source/drain The gate of the third transistor is controlled by a first control signal, the first source/drain of the third transistor is coupled to a first voltage, and the third transistor The two source/drain electrodes are coupled to one of the first source/drain of the first transistor, wherein one of the first transistors is coupled to the second source/drain The first end of the light-emitting element is coupled to a second control signal. The pixel driving circuit of claim 4, wherein the second driving unit comprises: a fourth transistor having a gate, a first source/drain, and a second source/drain. The gate of the fourth transistor is controlled by a third control signal, the first source/drain of the fourth transistor receives the data voltage, and the second source/汲 of the fourth transistor The pole is coupled to the gate of the first transistor; and a fifth transistor having a gate, a first source/drain, and a second source/drain, wherein the fifth transistor The gate is controlled by a fourth control signal, the first source/drain of the fifth transistor receives the data voltage, and the second source/drain of the fifth transistor is coupled to the first The second source/drain of the crystal, wherein the adjusting unit has a first end and a second end, the first end of the adjusting unit is coupled to the gate of the first transistor, and the adjusting unit The two ends are coupled to the source/drain of the first transistor. The pixel drive circuit of claim 5, wherein the first control signal, the second control signal, the third control signal, and the fourth control signal are at a high level during a precharge period; During a set period, the first control signal and the third control signal are at a low level, and the second control signal and the fourth control signal are at a high level; and during a lighting period, the first control signal is a high level, and the second control signal, the third control signal, and the fourth control signal are at a low level. The pixel driving circuit of claim 5, wherein the first transistor, the second transistor, the third transistor, the fourth transistor, and the fifth transistor comprise at least one depletion type Transistor. The pixel driving circuit of claim 5, wherein the first source/drain of the fourth transistor further receives a reference voltage. The pixel driving circuit of claim 1, wherein the first driving unit further comprises: a third transistor having a gate, a first source/drain, and a second source/drain The gate of the third transistor is controlled by a first control signal, and the second source/drain of the third transistor is coupled to a second voltage, wherein the first of the light-emitting elements is first The second end of the first light source is coupled to one of the first source/drain of the first transistor, and the second source/drain is coupled to the first transistor. To the first source/drain of the third transistor. The pixel driving circuit of claim 9, wherein the second driving unit comprises: a fourth transistor having a gate, a first source/drain, and a second source/drain. The gate of the fourth transistor is controlled by a third control signal, the first source/drain of the fourth transistor receives the data voltage, and the second source/汲 of the fourth transistor The pole is coupled to the gate of the first transistor; and a fifth transistor having a gate, a first source/drain, and a second source/drain, wherein the fifth transistor The gate is controlled by a fourth control signal, the first source/drain of the fifth transistor receives the data voltage, and The second source/drain of the fifth transistor is coupled to the first source/drain of the first transistor, wherein the adjusting unit has a first end and a second end, and the adjusting unit The first end is coupled to the gate of the first transistor, and the second end of the adjusting unit is coupled to the second end of the light emitting element. The pixel drive circuit of claim 10, wherein the first control signal is at a low level during a precharge period, and the second control signal, the third control signal, and the fourth control signal are a high level; the first control signal, the second control signal, and the third control signal are at a low level during a set period, and the fourth control signal is at a high level; and during a lighting period, the The first control signal and the second control signal are at a high level, and the third control signal and the fourth control signal are at a low level. The pixel driving circuit of claim 10, wherein the first transistor, the second transistor, the third transistor, the fourth transistor, and the fifth transistor comprise at least one depletion type Transistor. The pixel drive circuit of claim 10, wherein the first source/drain of the fourth transistor further receives a reference voltage. A pixel driving method is suitable for a pixel driving circuit, wherein the pixel driving circuit is configured to drive a light emitting component, and the pixel driving circuit comprises a first driving unit, a second driving unit and an adjusting unit. The pixel driving method includes: driving the light emitting element by a first driving unit, wherein the first driving unit comprises a first transistor; and the second driving unit provides a data voltage to the first transistor a body, wherein the first driving unit drives the light emitting element according to the data voltage; and adjusting a gate voltage of the first transistor by adjusting the unit, wherein the adjusting unit comprises a set capacitor and a second transistor, The set capacitor is coupled in series with the second transistor between the first driving unit and the second driving unit. The pixel driving method of claim 14, wherein in the step of adjusting the gate voltage of the first transistor, the gate voltage of the first transistor is adjusted by the set capacitance. The pixel driving method of claim 14, wherein the pixel driving circuit further comprises a storage capacitor coupled between the first driving unit and the second driving unit, the pixel The driving method further includes: storing, by the storage capacitor, the data voltage to one of the gates of the first transistor. The pixel driving method of claim 14, wherein the adjusting unit has a first end and a second end, and in the step of providing the data voltage to the first transistor, in a pre-charging During the period, the first end and the second end of the adjusting unit are respectively charged to the data voltage and a first voltage. The pixel driving method of claim 17, wherein in the step of adjusting a gate voltage of the first transistor, the second driving unit and the adjusting unit are used in a setting period. The first end of the adjustment unit is discharged to compensate for a threshold voltage value of the first transistor. The pixel driving method of claim 18, wherein in the step of driving the light emitting element, during a light emitting period, the threshold voltage of the first transistor is stored according to the set capacitance a first transistor to drive the light emitting element by the first voltage. The pixel driving method of claim 14, wherein in the step of providing the data voltage to the first transistor, a reference voltage is further supplied to the first transistor.